Two Line Gas Spectroscopy Calibration

Abstract

A method of calibrating an absorption spectroscopy measurement wherein the calibration method includes projecting laser light through a sample of a first quantity of a gas of interest and a second irrelevant quantity of a spectroscopically identical or similar gas (10). The first and second spectroscopic absorptions of the laser light are measured over specific first and second absorption lines. A functional relationship is determined between the first and second measured spectroscopic absorptions and two unknown variables. The function relationships may then be simultaneously solved to determine one or both unknown variables and thereby obtain a measurement relating to the first quantity of the gas of interest, calibrated for the second irrelevant quantity of gas.

Description

TECHNICAL FIELD[0001]The present invention is directed toward a method and apparatus for calibrating an absorption spectroscopy system and more particularly toward a method and apparatus for determining a gas concentration within a combustion chamber using tunable diode laser absorption spectroscopy in installations where supplemental gas is present in the spectroscopy path.BACKGROUND ART[0002]A large percentage of the electrical power generated in the United States of America is created in coal combustion power plants. The bulk of worldwide electricity production similarly relies on coal as a primary energy source. It is likely that coal will remain a primary energy source in the foreseeable future given the long term environmental concerns with the storage of waste from nuclear energy generation operations, and the inefficiencies associated with solar powered electrical generation. In addition vast worldwide coal reserves exist sufficient for at least 200 years of energy productio...

AI Technical Summary

Benefits of technology

[0010]One aspect of the present invention is a method of calibrating an absorption spectroscopy measurement where the probe laser path transverses both a quantity of the gas of interest, and a quantity of a spectroscopically similar or identical gas which is irrelevant to the desired measurement, but has the potential interfere with the measurement. The calibration method includes projecting laser light through a sample containing a first quantity of a gas of interest and a second irrelevant quantity of a spectroscopically identical o

Problems solved by technology

Extractive sampling systems are not particularly well suited to closed loop control of a combustion process since a significant delay can be introduced between the time of gas extraction and the ultimate analysis.

The plants are fired by pulverized coal, which results in a combustion process which both obscures the transmission of laser light because of the high dust load and which is extremely luminous.

In addition, various strong disturbances are found under power plant combustion conditions.

There is also intense thermal background radiation from the burning coal particles which can interfere with detector signals.

The environment outside of the power plant boiler also makes the implementation of a TDLAS sensing or control system problematic.

As described above, the interior of the combustion chamber is an extremely hostile environment full of pulverized coal, ash, and other particulate matter.

Thus, there is a tendency for the opening or port to become clogged or partially blocked with ash and other particulate matter.

The introduction of O2 containing purge gas significantly complicates this measurement.

Similarly any absorption spectroscopy measurement of a quantity of gas is complicated if a second quantity of the gas is also present in the measurement path.

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